Crate sefer_region 

sefer-region — typed handle-addressed store

A thin typed membrane over slotmap: values live in slotmap’s dense, cache-friendly, always-compact backing store, and every operation exposes only typed Handle<T> values — raw DefaultKeys never escape the crate boundary.

What makes this different from using slotmap directly?

Slotmap’s DefaultKey is untyped: a DefaultKey from one map can be passed to another of a different value type without a compile error. sefer-region wraps it in Handle<T> — a PhantomData<fn() -> T>-branded key — so the compiler rejects cross-region handle confusion at the type level.

Invariants upheld (I1–I5)

• I1 — resolution: a fresh handle resolves via Region::get to the inserted value until it is Region::removed.
• I2 — tombstone: after remove(h), get(h) is None forever; a second remove(h) is a no-op None.
• I3 — no ABA: a stale handle — one whose slot has since been reused — never resolves to a live value. slotmap’s DefaultKey carries a generation that is bumped on removal, so the old handle fails the version check.
• I4 — accounting: Region::len equals the number of live entries and Region::is_empty agrees.
• I5 — drop-once: every live value is dropped exactly once — on remove (returned to the caller) or on Region drop — never twice, never leaked.

Pure Rust / zero own unsafe

#![forbid(unsafe_code)] at the top of this crate. The internal unsafe in the slotmap dependency is its own, audited and battle-tested. This crate adds no C / C++ libraries and contributes zero unsafe blocks of its own.

no_std support

With default-features = false (disabling std) the crate compiles under no_std + alloc, providing Region<T> and Handle<T>. The std feature (on by default) additionally enables SyncRegion<T>, which wraps Region<T> in std::sync::RwLock.

Structs

Handle

An opaque, copyable reference to a value stored in a Region.

Region

A handle-addressed store of T.

SyncRegion

A thread-safe wrapper around Region<T> — the trusted concurrent baseline.